The invention relates to an active suspension system, particularly for vehicles, having supporting units, which each have an actively lift-adjustable regulating unit and a passive spring arranged in series thereto, and having an automatic control of the regulating units, a path sensor for generating a signal correlated with the lifting position of the supporting unit being assigned to each supporting unit, and an arrangement of acceleration sensors being provided on the vehicle body for generating signals for body-side longitudinal and lateral accelerations as well as lifting movements, and control signals used for controlling the regulating units comprising a first proportion generated by signals of acceleration sensors and a second proportion generated by signals of path and acceleration sensors.
A suspension system of the type generally described above is the object of German Patent Document DE 39 32 476 A1. According to this document, hydropneumatic spring and supporting units are provided in the case of which the passive spring is formed by a pneumatic spring loading device. This spring is hydraulically connected with a piston working space of a piston-cylinder unit arranged between the sprung and the unsprung mass, in which case the hydraulic "linkage" formed by the hydraulic connection can be lengthened or shortened by the feeding or removal of hydraulic medium.
The first proportion of the control signals is determined by the longitudinal and lateral acceleration by the vehicle body. The second proportion of the control signals depends on the lifting path of the unsprung mass relative to the sprung mass as well as the vertical acceleration of the sprung mass.
German Patent Document DE 42 31 641 A1 as well as German Patent Document DE 44 14 022 A1 show active suspension systems, in which a passive mechanical spring is arranged in series to a hydraulic regulating unit by means of which the lifting position of the unsprung mass can be changed relative to the sprung mass or lift adjustments can be generated which are superimposed on the spring lift of the passive spring.
From German Patent Document DE 41 39 412 A1, an active suspension system is known in which small, obviously hard passive springs are provided which are constructed only for influencing higher-frequency movements of the tire or wheel, which have lower amplitudes, and are constructed as hydropneumatic springs. These springs are combined with adjustable dampers.
German Patent Document DE 42 17 325 A1 relates to an active vehicle suspension in the case of which individual natural vibration forms of the body can be influenced separately from one another in the sense of a "Skyhook" damping.
According to German Patent Document DE 29 43 486 C2, it is provided to assign to each supporting unit of an active suspension system, in the case of which one lift-adjustable regulating unit respectively is arranged in series to a passive suspension; a path sensor for determining the regulating path of the regulating unit; as well as a vehicle-body-side acceleration generator for determining the body-side vertical acceleration. From the signals of the acceleration generator, in addition to the acceleration signals, other signals are determined by calculation for the vertical velocity and the vertical position of the vehicle body. The regulating units are then in each case controlled as a function of their lifting position as well as of the signals for the vertical acceleration, the vertical velocity and the vertical position of the vehicle body. As a result, a good damping of the vehicle body movements is endeavored.
In addition, it is basically known, for example, from German Patent Document DE 43 03 160 A1 to provide, in the case of chassis systems, only one actively controllable regulating unit respectively between the vehicle body and the wheel, without providing an additional passive spring arranged in series with the regulating unit and to carry out the controlling of these regulating units as a function of parameters to be monitored by means of a desired-value/actual-value comparison. Systems of this type must have an extremely high reaction capacity of the regulating units as well as of the regulating paths. Otherwise, because of the lack of flexible passive elements between the wheel and the vehicle body, the suspension action would be extremely uncomfortable.